Search

The 3D lanthanum-dicarboxylate MOF [La2(hex)3(H2O)4]3H2O, (1), (hex = trans,trans-muconic acid) has been obtained at 50 °C, in a silica gel column, either via in situ transformation of the 2D MOF [La2(hex)3(H2O)6]9H2O, (2), published previously, or directly. The structure is made up of metal–ligand layers pillared by a ligand dianion. The comparison of the crystal structures of the two MOFs allowed us to propose a possible mechanism of the 2D to 3D transformation. The presence of many short olefinic contacts allowed the formation of three photoproducts at different yields, the major one being the rtct isomer for the 3D MOF and the rttc one for the 2D MOF. In both cases, the three photoreactions proceed with the parallel reaction scheme. The comparison of the crystal structures of 1 and 2 allowed the photoreactivity differences observed to be explained.

A 2D lanthanum-dicarboxylate MOF of the formula [La2(hex)3(H2O)6]·9H2O (H2hex = trans,trans-hexadiendioic acid or trans,trans-muconic acid) has been synthesized by the silica gel technique. The structure consists of metal–organic layers separated by a 2D network of water molecules. The metal–organic layers are made up of La3+ arrays linked by the muconate ligands. Within a layer there is an infinite chain of short contacts between olefinic bonds allowing formation, upon UV irradiation, of three photoproducts. One of them was completely unexpected and its formation is explained by complex molecular movements in the solid state. The thermal instability of the MOF allowed isolation of five photochemically active lower hydrates. The rate constants of all hydrates were determined and show significant variations between them, attributable to structural rearrangements within the metal–organic layer brought about upon dehydration.

A 2D layered structure composed of Cd dimers, linked by fumarate anions to form a rectangular grid network, was pillared, via metal coordination, to afford a 3D photoreactive metal–organic framework.